Spacecraft-to-spacecraft radio occultations experiments are being conducted at Mars between the Mars Express (MEX) and Trace Gas Orbiter (TGO) spacecraft, the first ever periodic inter-spacecraft occultations at a planet other than Earth. Here we present results from the first 83 such occultations, conducted between 2\textsuperscript{nd} Nov 2020 and 5\textsuperscript{th} of July 2023. Of these, 44 observations have to-date resulted in the extraction of vertical electron density profiles. These observations are the successful results of a major feasibility study conducted by the European Space Agency to use pre-existing relay communication equipment for radio science purposes. Mutual radio occultations have numerous advantages over traditional spacecraft-to-ground station occultations. In this work, we demonstrate how raw data are transformed into electron density values and validated with models and other instruments.

Ionospheric total electron content (TEC) variations prior and after to the great Gorkha Earthquake in Nepal (Mw = 7.8) on April 25, 2015, were analysed using measurements from widely distributed Global Positioning System (GPS) network. This study has been performed to understand the relationship between ionospheric TEC anomalies and earthquake occurrences. The analysis of vertical TEC (VTEC) time series from different GPS stations shows that the abnormal TEC variations appeared few days up to a few hours before the events. The results indicate that deviation in VTEC observed on the distant GPS station from the epicentre was found less relative to that of the stations near the epicentre, inferring that the variation in ionospheric VTEC nearly inversely relies upon the distance of GPS stations from the epicentre. Moreover, the pre-earthquake ionospheric anomalies were also observed in the geomagnetically conjugated region. In view of the solar-terrestrial environment, the pre-earthquake ionospheric anomalies could be associated with the Nepal earthquake. The VTEC anomaly was identified when it crosses the upper bound or lower bound. The outcomes additionally show that TEC variation was dominant in the vicinity of the earthquake epicentre. We also describe contrast in TEC throughout the globe using global ionospheric maps at regular 2-hour UT intervals, the day before, during and after the earthquake. In addition, we observed that areas heavily influenced by TEC were found to be transposed from eastern sectors to western sectors through the equatorial plane.